Bevel modifier not working on SVG converted to mesh
Curve objects get really bad topology when converted to mesh. Boolean operations will also contribute to make the topology even worse.
And at the end the irregular and triangulated topology of the object will not let you bevel.
So keep the object as a curve.
Create the object, with the holes, in illustrator as a path (no need to use booleans).

Import the SVG into blender, do not convert to mesh.

To do the extrusion as curve make it a 2D curve, set the fill to mode  to &quot;both&quot;.

In the Geometry controls set the extrusion level and the bevel  as well.